We have an existing, large, application, for which we are going back and creating unit tests. We're starting with some of our core methods and then will expand this to include most internal and public methods.

Is there a best practice for keeping track of which methods in our application contain a unit test (or don't)? Perhaps an attribute or some other way? In other words, We'd like to be able to look at a method in our code and know if the method is under a unit test.

completely agree. indication that method has a test or not means nothing. often 1 method requires many tests (e.g. parameterized tests) so coverage is much more valuable information. and you don't have to look at your code - you should look at reports (e.g. sonar for java)
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piotrekDec 24 '12 at 12:59